Some drinking drivers apparently do not manifest typical symptoms of intoxication, even at blood alcohol concentrations (BAC) well above the legal limit, assumedly because of increased tolerance/adaptation to the impairing effects of alcohol developed through their extensive drinking. If such drinking drivers exist, how many and who are they? Do they disproportionately escape police detection? The proposed research is designed to address these questions through use of voluntary research surveys (involving 42,000 drivers) conducted at roadside during high-risk nocturnal times. Consenting drivers will be screened for breath alcohol using the new "passive alcohol sessor." Three field sobriety tests will be used to assess alcohol tolerance. All high BAC drivers, plus a sample of all other drivers, will be invited to provide an extensive interview in the near future. The specific aims consist of determining: (1) the prevalence of drivers with high alcohol tolerance, and their salient characteristics; (2) the prevalence of "social" drinkers and "problem" drinkers among high BAC drivers; (3) the differences in characteristics between high BAC drivers arrested and not arrested for DUI; (4) the effectiveness of current specific deterrents for drunken driving; and (5) the relative effectiveness of chemistry- based vs. behavior-based enforcement of DUI laws. The answer to these main study questions will be accomplished through multivariate analyses of 5 domains of data: (1) self- reported background data, plus drinking, driving, drinking-and- driving information and attitudes, and selected personality characteristics; (2) driver record, both pre- and post-contact; (3) BAC at roadside; (4) performance on the most valid "field sobriety tests:" (gaze nystagmus, walk-and-turn, and standing steadiness); and (5) the clinical signs of intoxication. Long-term objectives: The proposed research is designed to augment an ongoing project concerned with determining the probabilities of drunken driving both among the U.S. driving public and among convicted DUIs. Together the projects will enable developing a statistical profile for the high tolerance/adaptation driver and almost all other segments of the drinking-and-driving population which should facilitate: (1) early identification of such drivers for referral purposes, (2) development of customized prevention strategies and programs, and (3) obtaining further data regarding possible generic factors in high tolerance/adaptation to alcohol.